The present invention relates to resource allocation in wireless communication systems. More particularly, and not by way of limitation, the present invention is directed to a system and method for scheduling users in a Frequency Division Duplex (FDD) wireless system with duty cycle limitation.
A wireless communication system (e.g., a cellular telephone network) may be an FDD wireless system in which uplink transmissions (e.g., transmissions from a mobile device to a base station in a cellular network) and downlink transmissions (e.g., transmissions from a base station to a mobile device in a cellular network) may use different frequency bands, but both the transmissions are possible simultaneously (i.e., in a duplex manner) in the assigned frequency bands (or telecommunication channels). Generally, both the uplink and downlink transmissions work with a 100% duty cycle—i.e., a mobile device (or user equipment (UE)) and a network node (e.g., a base station or an eNodeB (enhanced Node B or eNB)) transmit power all the time when active.
FIG. 1 identifies an exemplary radio frame 10 having a 100% duty cycle. FIG. 1 illustrates one radio frame 10 (Frame N) in a sequence of radio frames (Frames N−1, N, N+1, etc.) that may constitute the communication “link” between the network node (e.g., eNodeB 36 in FIG. 3, which is discussed later hereinbelow) and the mobile devices (e.g., the UE 32 in FIG. 3) in the wireless network (e.g., the carrier network 34 in FIG. 3). The radio frame 10 may be of a fixed duration and may be divided into a fixed number of equally-sized subframes identified as subframes “S0” through “S9” in FIG. 1. For example, in case of an LTE (Long-Term Evolution) network, each radio frame 10 (i.e., each of Frame N, Frame N+1, etc.) may be of 10 ms duration, and may contain 10 subframes of 1 ms each as shown in FIG. 1. The frequency bandwidth of the radio frame 10 may depend on the overall system bandwidth available in the carrier network. When a mobile device is active in an FDD carrier network, it operates at 100% duty cycle and it may transmit power in each subframe as shown in FIG. 1. In case of the LTE network, the subframe duration of 1 ms may be referred to as a Transmission Time Interval (TTI). Thus, in a 100% duty cycle operation, there may be ten TTI's in each frame 10 as shown in FIG. 1. The eNB may schedule a mobile device to use different TTI's to transmit different contents (e.g., TTI-1 to transmit requests for network resources; TTI-0 and TTI-5 to receive synchronization signals from eNB; TTI-3 to transmit channel-related information; TTI-5, TTI-6, and TTI-7 to transmit voice and text messaging content; etc.). The scheduling by eNB may involve providing necessary channel (frequency) resources to the mobile device to enable the mobile device to carry out communication with the eNB. In any event, in case of a 100% duty cycle operation, the mobile device continues to transmit power during all TTI's even when no voice/data or other content is transmitted/received during a particular TTI.
However, there are some instances where the mobile device (e.g., the UE 32 in FIG. 3) or the network node (e.g., the eNB 36 in FIG. 3) work with some duty cycles less than a 100% duty cycle. For example, the Wireless Communications Service (WCS) band in the frequency spectra of 2305-2320 MHz and 2345-2360 MHz is allotted by the Federal Communication Commission (FCC) to provide fixed, mobile, radiolocation or satellite communication services to individuals and businesses within their assigned spectrum block and geographical area. The frequency spectra of the WCS band are divided into four blocks (A, B, C, and D) of 5 MHz and 10 MHz sizes. The WCS is capable of providing advanced wireless phone services (e.g., services that are able to pinpoint subscribers in any given locale) and can also support an entire family of new communication devices utilizing very small, lightweight, multi-function portable phones and advanced devices with two-way data capabilities allowing subscribers to send and receive data, video messages and/or other multimedia/broadband content without connection to a wire. However, a mobile device operating in the WCS band may cause interference with adjacent bands (e.g., bands assigned to commercial satellite radio broadcasts). Hence, to reduce or limit interference with adjacent bands, the FCC has mandated that each mobile device operating in the WCS band may have a maximum duty cycle of 25% in blocks NB of the WCS band and 12.5% in blocks C/D of the WCS band.
FIG. 2 identifies two exemplary radio frames 14, 16 implementing a 25% duty cycle power transmission from a mobile device. It is seen from FIG. 2 that a mobile device operating in a wireless band (e.g., the WCS band discussed above) having a 25% duty cycle restriction may transmit power in only a selected number of TTI's in each frame—e.g., TTI-0, TTI-4, and TTI-8 in Frame N; and so on. In other words, in case of FIG. 2, the mobile device may transmit power in every fourth TTI after the initial TTI to maintain the required 25% duty cycle, and, hence, may not be able to transmit any content in the remaining TTI's in which no power is transmitted. As another example, in case of a 20% duty cycle (not shown), the mobile device may transmit power every fifth TTI after the initial TTI—i.e., only two TTI's per frame are used for content transmission/reception. Other duty cycles (less than 100%) may be similarly implemented.